I guess you mean handling mods like this?
Well, it's not very difficult, just find GTA Vice City folder, go to data, and find handling.cfg
Then, open it with notepad and start changing the numbers there. I recommend to backup your original file, just in case it crashes. And remember, before you start modding, right click handling.cfg and check it's not "read only" If it is, you can't mod it. You can PM me everytime on GTAForums if you need help!